The standardization of femto base station or the so-called home base station is an ongoing process in 3GPP. The femto base stations are to be deployed in home, in office or in other private premises and is a radio base station adapted to cover a small area such as a home or similar place. An operator may choose to share the same carrier between femto base stations and macro/micro/pico base stations (i.e. non femto base stations) or alternatively assign a dedicated carrier only for femto base stations. Particularly, in the former scenario unnecessary high transmission power level of the femto base stations may severely impact the macro base station. Therefore the transmit power of the femto base station needs to be properly regulated.
The terms femto base station, home base station, home Node B, home 3G Access point or home eNode B refer to the same type of base station in principle. For simplicity the term femto base station will be used hereinafter.
In FIG. 1 is shown a block diagram illustrating a Wideband Code Division Multiple Access (WCDMA) network including femto base stations. The wireless communications network 1 includes a core network (CN) 2 connected to a radio network controller, (RNC) 3, using a standard Iu interface. Alternatively, the RNC is a Macro RNC and/or a Femto RNC. The RNC controls all Radio Base Stations that are connected to the RNC, both Macro and Femto Radio Base Stations. In the figure, the RNC 3 is connected to a Macro Radio Base Station (RBS) 4 and to one or more femto base stations 6 belonging to a group of femto base stations 5. The interface between the femto base stations and the RNC is a Iub+ interface or an Extended Iub interface, and is transported using an Internet Protocol (IP) network providing IP connectivity between a femto base station and the RNC. As this IP network may consist of unprotected IP networks, security mechanisms between the RNC and the femto base stations are included. Communication between the RNC 3 and the Macro RBS 4 is IP based or IP/Asynchronous Transfer Mode (ATM) based, and the interface is Iub. The Macro RBS 4 is working as an access point for one or more mobiles 9 within a macro cell 7. The group of femto base stations 5 are working as access points for mobiles within femto cells 8. The RNC 3 may also communicate with a femto base station 6 via the Macro RBS 4. This way the femto base station uses the Macro RBS as a wireless access point into the core network. An Operation Support Systems (OSS) 12 usually performs management of access points, Macro RBSs. A femto base station manager 13 is responsible for managing the femto base stations. The OSS and the femto base station manager can be stand alone nodes or parts of other nodes like the RNC 3 or the CN 2. The OSS and the femto base station manager can also be distributed programs in a network 1.
The following sections describe various concepts and technological aspects, which are used or are related to the present description.
Femto Base Station
In legacy UTRAN specifications three classes of base stations are defined, see third generation partnership project (3GPP) Technical specification (TS) No. 25.104, “Base Station (BS) radio transmission and reception (FDD)”:                Wide area BS; it serves macro cell deployment.        Medium range BS; it serves micro cell deployment.        Local area BS; it serves pico cell deployment.        
Femto base stations are being developed to serve even smaller and more localized areas than the pico cells. Femto base stations operate under licensed frequency band and are currently under standardization within 3GPP.
In WCDMA, the femto base station maximum output power is proposed to be limited to 20 dBm for non Multiple Input Multiple Output (MIMO) case or 17 dBm per antenna port in case of MIMO (2×2).
In general these different base station classes differ due to different minimum coupling loss in different environments. Secondly they typically operate at different maximum output power levels. For instance wide area base stations operate at higher maximum output power than the medium range and so on. These factors in turn lead to different performance requirements for different base station classes. These requirements are defined in 3GPP TS 25.104, “Base Station (BS) radio transmission and reception (FDD)”.
One main difference compared to other base station classes is that the Femto base station is owned by a private subscriber, who is at the liberty to install at any location. Thus, strict network planning is not possible in case of femto base station network. This is in contrast with other base station classes, which are deployed by an operator according to some well defined principles. The lack of precise network planning of femto base stations may cause interference to other base stations.
Femto Base Station Implementation Aspects
A femto base station comprises of normal base station functions such as transmitting and receiving signals to and from multiple User Equipment (UE). In addition it can comprise a normal UE receiver circuitry for performing measurements, which in turn can be used for adjusting its output power level. This UE receiver circuitry is compliant to the UE performance requirements specified in the relevant UE specification.
Femto Base Station Deployment Scenarios